Planetary Radio • Aug 16, 2023

JWST detects water vapor in a planet-forming disk

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On This Episode

Giulia perotti portrait

Giulia Perotti

Postdoctoral fellow at the Max Planck Institute for Astronomy

Thomas henning portrait

Thomas Henning

Director of the Max Planck Institute for Astronomy, co-principal investigator of JWST’s Mid-Infrared Instrument (MIRI), principal investigator of the MIRI Mid-Infrared Disk Survey (MINDS)

Ariel barreiro headshot

Ariel Barreiro

Communications Intern for The Planetary Society

Bruce betts portrait hq library

Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

Sarah al ahmed headshot

Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

A team of researchers using the James Webb Space Telescope (or JWST) has made the first detection of water vapor in the inner region of a protoplanetary disc that is already forming worlds. Giulia Perotti and Thomas Henning from the Max Planck Institute for Astronomy in Germany join Planetary Radio to discuss their team's research on PDS 70 and what it can tell us about the formation of planets like Earth. The Planetary Society's most recent intern, Ariel Barreiro, reflects on her summer working with The Planetary Society, and Bruce Betts, our chief scientist, pops in for What's Up and a conversation about terminator zones.

PDS 70 concept art
PDS 70 concept art This artist’s concept shows the star PDS 70 and its protoplanetary disk. Data taken by JWST have detected water vapor in the inner region of the disk, an area where rocky worlds may be forming. This is the first detection of water in the terrestrial region of a disk that is already known to host two or more protoplanets.Image: NASA, ESA, CSA, J. Olmsted (STScI)
PDS 70 Spectrum
PDS 70 Spectrum The graphic shows the spectrum of PDS 70, a young star system with a protoplanetary disk that is actively forming worlds. The JWST data show the detection of water vapor in the inner part of the disk, a region where rocky, terrestrial worlds may be forming.Image: NASA, ESA, CSA, Joseph Olmsted (STScI)
Artist's rendition of an exoplanet with a terminator zone
Artist's rendition of an exoplanet with a terminator zone Worlds with terminator zones could be places to explore in the search for life.Image: Ana H. Lobo


Sarah Al-Ahmed: How do rocky worlds get their water? New data from JWST adds another piece to the puzzle. This week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our solar system and beyond. A team of researchers using the James Webb Space Telescope or JWST has detected water vapor in the inner region of a proto-planetary disk that is already forming planets. Giulia Perotti and Thomas Henning from the Max Planck Institute for Astronomy join us to talk about the team's research and what it might be able to tell us about the formation of worlds like Earth. But first, you'll hear from The Planetary Society's most recent intern, Ariel Barreiro as she reflects on our summer working with our team. Then Bruce Betts, the chief scientist of The Planetary Society will join me for what's up and a conversation about Terminator zones. Here at The Planetary Society, we believe that space is for everyone. No matter who you are or where you come from on this planet, we all deserve to know more about our place in space and have opportunities to work in the field if that's what we choose to pursue. As part of our organization's commitment to making the space community more inclusive. We've been very lucky to have a series of wonderful interns from the Zed Factor Fellowship join our teams. Ariel Barreiro, our most recent intern, just ended her time with us last week. She's here to talk about her summer at The Planetary Society and what fellowship programs like Zed Factor can do to help people from underrepresented groups find their place in the space industry. Hey, Ariel.

Ariel Barreiro: Hi.

Sarah Al-Ahmed: It's so funny because I feel like your time with us has gone by so fast.

Ariel Barreiro: Really fast.

Sarah Al-Ahmed: Yeah. You just started what, in June?

Ariel Barreiro: Yeah. It feels like the blink of an eye now though.

Sarah Al-Ahmed: It really does, but you're our most recent intern from the Zed Factor Fellowship. Would you mind sharing what that organization does?

Ariel Barreiro: The Zed Factor Fellowship is great. They are helping underserved community members get into the space sector.

Sarah Al-Ahmed: It's so important. There are so many people that deserve this opportunity, and classically there have been so many barriers in the way for these underrepresented groups, yourself and myself included, to get into this field. So anything we can do to try to help people out is great.

Ariel Barreiro: Yeah, I agree. They were really great too, because they opened it up past just engineering, so they opened up for anybody in communications, marketing. I think we even had a student who didn't really have any aerospace background at all that was able to come in and get involved. So I think that's really, really big.

Sarah Al-Ahmed: What kind of opportunities does it provide for people?

Ariel Barreiro: So they match you with a host company and depending on your background, you interview and then see who works best with you. They also place you with two mentors, and I have to say they just did such a great job. I'm going to shout out Sarah Mineiro a little bit. She works in defense and she was mine, and we just clicked really well, and then obviously I clicked really well with everybody at The Planetary Society, so I think they do a really great job placing students with a host company that suits them.

Sarah Al-Ahmed: What in your life led you on this journey that ultimately put you with us at The Planetary Society?

Ariel Barreiro: So I'll try to keep it short, right? I'm older, so that's my non-traditional burden to bear, and I have been in restaurants for the last 20 years and at some point when you're in that industry, you reach the top and realize there's nowhere else to go, and do you really want to do this backbreaking work for the next 30 or 40 years? So I decided to switch out. I had a really great high school physics professor that kind of always stuck with me, and then I just got really lucky along the way. Honestly, I met women in physics, women in astronomy that just helped me every step of the way stay involved and push through getting a degree later in life.

Sarah Al-Ahmed: That's so cool. Do you have any aspirations for what you want to do in the field later?

Ariel Barreiro: I have no idea. I feel like I learned so many new avenues being here and through the fellowship that now where it was just scientific journalism now I see so many different paths. I will say a very long-term goal of mine is to work in the White House though for sure now that I've seen it.

Sarah Al-Ahmed: I love that. Are you making any plans to potentially go to our Day of Action in Washington DC? Because I feel like that would be a great opportunity to see what that's all about.

Ariel Barreiro: Oh my god, yes. Big time. I've been like on Jack like, "I'll be there. I'm going to help you. I can't wait to come and be a part of this." So yeah, I absolutely plan to be there for that.

Sarah Al-Ahmed: That's awesome. I'm really looking forward to it myself. So what's your time at The Planetary Society been like?

Ariel Barreiro: Life changing. Oh my gosh. The Planetary, Society, I'm going to shamelessly plug you on your own platform, but just what an amazing group of people. I immediately felt comfortable meeting all of you. You were just also welcoming and then working with Ray specifically, she is a wealth of information as far as science communication is concerned, and she didn't hold back and giving me that information and just any question I had, she had an answer and anytime I'd do something, she'd just very diplomatically show me a better way to do things. So it's just been a really great experience. I'm so sad that it's over.

Sarah Al-Ahmed: Yeah, Ray Paoletta is our associate producer for the show, but also our editorial director here at The Planetary Society. And I'll shout her out as well because she's done so much for me recently during this transition into Planetary Radio and being someone there that I can count on to help me get through it. And that's really what it's all about. If we want to make people feel safe in the space community and make it more welcoming for other people, we've got to lift each other up and be kind to one another because we're all on our learning journey no matter where we are.

Ariel Barreiro: I think that's honestly one of my biggest takeaways from working with The Planetary Society, and I said this in the beginning and it held through the whole 10 weeks that I was with you guys, is just the amount of respect that I see interplayed between everybody that works here, the way that everybody talks about their job and the work culture. Again, I'm old enough to know a good one when I see one and this is like topnotch. Just the way everybody feels about their positions about the company, a company that's really true to its mission and vision statement. It's really great to see and be a part of.

Sarah Al-Ahmed: That makes me so happy to hear. But I know behind the scenes you've been working on some of our cool communications work and you just came out with your first article on our website. What's it called?

Ariel Barreiro: Oh my gosh, the whole title. I know it's about Terminator zones, it's our Terminator zones, our next Search for Life. This wasn't necessarily something scientists were looking at before and over the last few years they've started to think, "Maybe we should check this out."

Sarah Al-Ahmed: I love this concept. We can't get deep into this article right now because we're time limited, but if you want to learn more about Terminator Zones, I'm going to link to Ariel's article on this page for this episode of Planetary Radio. So if you want to read it's at and it's awesome.

Ariel Barreiro: Thank you.

Sarah Al-Ahmed: Thanks for being here with us, Ariel, both on the show and as one of our interns, and I cannot say it enough. I really, really can't wait to see what you do next, and I wish you all the luck in the future.

Ariel Barreiro: Oh, thank you so much. Thank you for having me. It's really been a blast. Pun intended.

Sarah Al-Ahmed: And now, for our main topic of the day, water and the formation of rocky worlds. Water is a necessary ingredient for life on earth, at least as we know it, but we still aren't 100% sure how our planet ended up with its vast oceans. We can't take a time machine back to the beginning of the Solar System as much as we want to, but as our technology improves, we can study other young star systems as they form their first worlds and that can give us some insights. Our guests today are Dr. Giulia Perotti and Dr. Thomas Henning from the Max Planck Institute for Astronomy or MPIA in Heidelberg, Germany. They've made a discovery that can help us learn more about how rocky planets get their water. While observing a planetary system with JWST called PDS 70, which is 370 light years away from Earth, they detected water vapor in the inner part of the proto-planetary disk. That's the region of the disk where rocky or terrestrial planets might be able to form. PDS 70 is already home to two known gas giants, so that makes this the first detection of water in the terrestrial region of a planet forming disk that already has two or more planets. Giulia Perotti is a postdoctoral fellow at the MPIA and the lead author on this research paper. Her studies focus on the astro chemistry of young stars and their inner planet forming discs. Her co-author Thomas Henning is the director of the MPIA. He's the co-principal investigator for JWST's mid-infrared instrument or MIRI, which was the instrument that made this detection. He's also the principal investigator of the MINDS Program. That's the MIRI mid-infrared disk survey. That's the survey that took the data for this study. PDS 70 is just one of the many star systems that they're investigating. Their paper called Water in the Terrestrial Planet Forming Zone of the PDS 70 disk was published in Nature on July 24th, 2023. Hi Giulia and Tom, thanks for joining me.

Giulia Perotti: Hi Sarah. It's a great pleasure to be here.

Thomas Henning: Hi, Sarah. Thanks for having us.

Sarah Al-Ahmed: It's funny because I feel very personally invested in the story, surely not as much as both of you since you work on it, but for many years, I taught a school program at an observatory and part of what I did was I presented the show to children about the role that water plays in our search for life and how comets might've been the vehicle that brought water to earth. And if I had known the results of your paper, it would've completely changed my storytelling. So Giulia, you're the lead author on this paper. So what did your team discover?

Giulia Perotti: So we pointed the JWST space telescope to a very young star in the constellation of Centauri that is called PDS 70. And while this star is not alone, it has a disk that it's composed of interstellar dust and gas, which is the birthplace of planets. And this is a very cool system because this is the first one where we detected with direct imaging two giant planets during the formation in the making. We used JWST to study the innermost regions close to the star, so an inner disk close to the star and we detected water vapor. We detected a substantial reservoir of water vapor there. So this is what JWST allowed us to discover this year.

Sarah Al-Ahmed: How did you both become involved in this project?

Thomas Henning: Well, it has a long history. I was getting involved in JWST more than 20 years ago. I'm actually a co-PI of one of the instruments MIRI, and we provided the mechanisms for the instrument, and as a return we got guarantee time. I'm leading one of the biggest projects of this guarantee time to study the inner disk of these planet forming regions and PDS 70 was the obvious choice because we were the team, we discovered the planets, so we also wanted to know what's going on in the disk.

Giulia Perotti: I'm a postdoc fellow at the Max Planck Institute for Astronomy in Heidelberg, and I work in the team led by Thomas Henning. And so I was really glad to be able to work on this beautiful data set and join efforts in getting a better understanding of what is the chemical composition of the terrestrial planet forming zones in protoplanetary disk such as PDS 70. So together with Thomas involved in what it's called MINDS Survey, MIRI Mid-INfrared Disk Survey, that is a, what is it, JWST GTO program that will probe 51 disks, thus we'll be able to gather a much better understanding of physical structures of the discs in the Mid-Infrared and the chemical composition where planets similar to our earth form.

Sarah Al-Ahmed: I love these kinds of collaborative projects, because I mean, you are the principal investigator for MINDS, right? Tom?

Thomas Henning: Yes, I am. But I also have a cool eye, Inga Kamp from the University of Groningen and of course quite a number of very active postdocs and PhD students are part of our program. PDS 70 is only one of the many results we are getting at the moment. There are other very interesting results we are obtaining and I think JWST is a great instrument because provides a sensitivity and also a SPECT resolution to define the molecular emission in these inner disks. Despite the fact that the telescope isn't large enough to dissolve these regions, we can nevertheless get information about the molecular content of the inner disks.

Sarah Al-Ahmed: JWST is really changing up our ability to study these systems and not just figure out the composition of planet forming disks but even analyzing the atmospheres of planets when we find them, which is just a complete game changer. Giulia, why did you choose to study this star system in particular for the study?

Giulia Perotti: Well, so this is an iconic disk in the planet [inaudible] community for some of the reasons we mentioned earlier, but this is the really first disk where we detected two giant planets in the gap that separates the inner disk that I've been studying with an outer disk. And these two giant planets have been directly imaged using VLT. These are called PDS 70b and PDS 70c. And so this young protoplanetary system is even more attractive to the community because towards planet PDS 70c, also at circumplanetary disk has been detected where exomoons may be forming. And so I was really extremely curious in looking at the inner disk of the system where planets like Earth may be forming right now. And so it was an obvious choice for me. It's definitely my favorite target in the survey.

Sarah Al-Ahmed: It's always cool to be able to take up an instrument as powerful as JWST and then study one of your favorite star systems. That's so exciting. For a long time the prevailing hypothesis has been that rocky planets form closer and toward their stars and then later they're seated by water with comets and other icy bodies that form further away and then migrate in and impact these objects. So why was that the assumption for so long?

Thomas Henning: I think we have actually two competing theories for the delivery of water. One indeed was that delivery by comets, but actually more by asteroids would be the source of water. The other theory was that small particles, small silicate particles containing water would bring the water early to the Earth and so the Earth formed to wet instead of dry. The reason why we saw that asteroids are the main source of water is simply that the Earth formed in a region we would not expect to have water at the time of formation. And on top of that, you also know that the isotopic composition, the ratio of heavy water to normal water in the asteroids is very similar to the ocean water on earth. So that was another reason that we saw that asteroids are important and that could still be the case today. So it's not that this is no longer a valid theory, but with our discovery we actually found that there's also water early on in the zone where the Earth could form and we now have to find out where the water actually came from. This is a real puzzle triggered by our observations.

Sarah Al-Ahmed: And that is the question for me because there's two ways that this could have occurred. Either the water is forming in the inner region of this planet forming disk or a similar situation where it's forming an ice further away and then migrating in toward this inner part of the stellar system. Which of these two scenarios do you think is most likely?

Giulia Perotti: With the current data, we cannot exactly say that one rules out the other. We tend to prefer the possibility that well, we can have transport of gas from the outer part of the disk to the inner part of the disk. So if oxygen rich gas can populate the inner disk and therefore sustain the inner disk, then if we have oxygen atoms there and we know that the inner disk of PDS 70 is rich in hydrogen, then we can form water in the gas phase. We can form water vapor as you said, and we know water molecules being UV absorbers so they can shield the water reservoir from the UV radiation from the star. So this viable scenario together with the dust coming from the outer part of the disk and filtering through the gap and reaching the innermost disk regions, also small dust particles, ice rich particles could couple with the gas populate the inner disk. But in that case we would really have the silicate to play a major role to track some of these water ice to higher temperature and therefore assure that even a temperature like 600 K, 500 Kelvin, the water is still preserved and then what sublimates at these temperatures together with the silicates. So I think this paper starts offering a clue and the take of messages that there is water in the innermost regions of disks that are cool and faint like PDS 70 and that they host planets. And right now we have to continue investigating the spectrum and investigating other systems and PDS 70 with all the other instruments of onboarding of JWST to be able to disentangle which of these two mechanisms plays the biggest role.

Sarah Al-Ahmed: Because we've got a scenario here where there's an inner disk and an outer disk that's separated by this large gap with protoplanets in between. Would that make it any more difficult for the silicates to transport water into the inner disk?

Giulia Perotti: We know that this gap where the two giant protoplanets are currently assembling is gas and dust depleted. And so we know from several observations and also modeling that a substantial amount of dust is not filtering through this gap. This is something that would speak for also the other mechanism. So filtering of the gas, oxygen-rich gas to play a role here.

Sarah Al-Ahmed: What kind of star is at the heart of this star system and how might that influence how much water vapor we see in the inner disk?

Thomas Henning: There's actually a star which is very similar mass to the sun, a little bit less massive but still comparable at 0.8 Solar masses, but it's very young as Giulia already alluded to. So the age of the system is about five million years compared to 4.567 billion years of the Solar System. So it's really a baby system and I think it's also important to realize that these systems are surrounded by two types of dust particles or solid particles. One which is very small, around a micron, smaller than the hair, which is very well coupled to the gas and the other one which we call pebbles, which are much larger, centimeter in size, which are actually decoupled from the gas, move from the outer to the inner disk. And indeed a big gap makes it very difficult for these pebbles to cross, but the smaller particles could cross and they could actually bring the water to the inner zone and they could also bring water to relative warm regions because silicates, at least some silicates, the property to contain water and bind water even higher temperatures. But the system is a very young one and it was actually discovered many years ago in a survey to find new young stellar objects and this was triggered by another satellite by IRAS, which was the first infrared satellite to do surveys and then put up work at a variety of observatories, try to find these young stellar objects. And that was one which was actually discovered, discovered by astronomers in Brazil using relatively small telescope and confirming that this is a young stellar object.

Sarah Al-Ahmed: It's only 5.4 million years old but it still has this very predominant planet forming disk. Is that a timescale on which we expect to still have a planet forming disk around a star?

Thomas Henning: This is a very good question. So if you would've asked me this question many years ago, I would have clearly answered no, because we saw that planet formation would be a much longer process. But now with the system, we know that these two giant planets were formed within five million years, so very rapidly, very early. And the average age of these systems of these disks is about three mega years. So up to three mega years, the disks are gone on average. Of course, we find older systems like TW Hydrae which has an age of 10 mega years in younger systems, but on average, after three mega years, the disks are gone and that means that we want to form planets they should have formed within this relatively short period of time.

Sarah Al-Ahmed: Is there any reasons that we can think why this disk still exists at this point in the stars' lifetime?

Thomas Henning: Yeah, as I said, I mean we have a variety of disk ages and some are a little bit older, some are a bit younger. That very much depends on the radiation environment from the young stellar object, but also on the stellar environment. If you would be in an environment which is very dense in terms of a lot of stars and the interactions may actually lead to shorter lifetimes, but this object has a quite average lifetime. I think we already see that the planet formation in the gap is nearly finished, we call the accretion rates, the amount of matter falling onto these planets is extremely small. They will not grow a lot in the coming decades or hundred years or millions of years because there is no longer any material or very little material around despite the fact that one has circumplanetary disk. So one can argue that the formation of the giant planets is practically done. What is going on in the very inner disk apart from our water detection, we don't know. We have still to find out if there are actually [inaudible] in the inner disk. It would be a very challenging observation.

Sarah Al-Ahmed: Yeah, it's always very difficult to find smaller planets, even with an instrument as powerful as JWST, it's always way easier to find the giant planets, which is a little sad because those rocky terrestrial planets are the ones that we really want to study if we want to find earth-like planets. But Giulia, is it possible that the water in this planet forming disk is still there because the star itself is a smaller star that might not be putting out as much ultraviolet radiation?

Giulia Perotti: Besides the water vapor detection, there is a lot to learn still using JWST in particular also the NIRCam and NIRSpec to understand the structure of inner disk and also with other high solution ground-based facilities to star itself, understanding whether there are stellar winds constraining. Even better, what is the UV flux of the star? So there are a lot of missing pieces to this puzzle, but with JWST we are starting unveiling some of the secrets of the inner disk.

Sarah Al-Ahmed: That's the exciting thing. If we study enough of these star systems, then maybe we can start to get an idea of which star systems are better for having water vapor in these regions or find that these larger patterns that can tell us more about these exoplanetary systems that we're only beginning to be able to study. Thomas, in your paper you make comparisons between PDS 70 and a star system called [inaudible]. Why is that a good star system for us to compare these findings to?

Thomas Henning: In general, I think we are interested in placing a discovering context with other objects. We now have observed close to 20 low mass solar type young stellar objects, so-called deuterized stars which have disks. And the nice feature of our program is now that we have disk which are small and large, disk which have various masses and also different [inaudible] environments, and one hypothesis is actually that large disks would need longer time in order to transport the pebbles from the outer disk to the inner disk and they should have less water. We now have discovered a disk which actually has a large disk which has a lot of water in the inner regions. So we now will be able to have a more comprehensive picture or the water distribution in the disks around these young stars. And the comparison star is just one possibility among many I would say.

Sarah Al-Ahmed: Is this a situation where you've taken data on many different star systems with JWST, but you've only kind of crunched the numbers on this one star system or did we just not find water vapor in the same regions in these other star systems?

Thomas Henning: No, no, no. We have now seen a number of optics where we see water vapor, but the PDS 70's only system where we know that there is actually a planetary system and where we have image the inner disk, but we know other systems which are similar but which we don't have seen the planets yet. We are still hunting for the planets on other systems, but we have seen water in quite a number of objects now that was actually already discovered by Spitzer, but now we see it in florid detail and we will find out how the water is actually transported to the inner disk. We not only see water, we also see something which I find extremely surprising that we see hydrocarbons and even benzene in this around low mass stars and brown dwarves. And that is really very strange because you also would expect oxygen rich material in these environments. But we do see completely different conversations.

Sarah Al-Ahmed: That is very interesting. And the complexity of these molecules that we're detecting can tell us a lot about their development, but we definitely need more data. I wish we had an entire bank full of just every star system we'd studied in the composition, but we're limited in time with what we can observe with JWST unfortunately.

Thomas Henning: I think we already have quite a good collection. At the end of our program, we will have observed about 60 to 70 objects. Other colleagues will observe additional sources. We already have a very nice program accepted for [inaudible], so I think we will get a very comprehensive picture. And on top of that, we are hunting for more directly image planets both from the ground and with JWST. So I think the real goal is of course to connect these birthplaces with the properties of the planets. I think that is a hot topic and the exoplanet community and the community of people investigating that information process.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Giulia Perotti and Thomas Henning after this short break.

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Sarah Al-Ahmed: Are there currently any other ground base or space observatories that are looking at this system in particular to try to follow up on these results?

Giulia Perotti: Well, when it comes to PDS 70 progress, for example, very large telescope, it's been looking at this system, observing the system, also targeting the inner disk, but different wavelengths compared to what we did with JWST. So definitely providing complimentary high resolution data for example. And as I was mentioning earlier as part of the MINDS Survey, so NIRSpec observations of PDS 70 have been taken and of NIRCam. So this system will be observed with all four instruments on onboard of JWST. That's why it's particularly exciting because for this particular system can use all the great capabilities of [inaudible].

Sarah Al-Ahmed: How long is it going to take for this project to complete, to study all these different star systems?

Thomas Henning: Yeah, I think we should have completed the program in terms of observations in summer next year. We get such amazing harbors that it will take a couple of years to publish everything and to investigate everything. I think we have really a wonderful data set and the next paper is already submitted or coming out. I guess the next two to three years will keep us busy.

Giulia Perotti: The spectra extremely rich as we're talking about. It's amazing to see first of all and at the same time requires a detailed analysis and also development of tools to perform an accurate interpretation of the result. But it's really great to see all this data coming in and we're constantly surprised when we start looking at the new dataset that JWST provided us with.

Thomas Henning: Yeah, we mainly talked about the gas, but we also get of course a lot of information about these small solid particles. And in this particular system, we have seen that, yeah, but more for silicates but also crystals. Actually some of the crystals have a color very similar to the green beach in Hawaii. I mean, the olivines and they tell us a lot about the thermal history of these disks and that's also another topic of research we have at the moment. So it's not just the gas, it's also the dust and both components together are important ingredients of the planet formation process.

Sarah Al-Ahmed: And that's an important thing to note as well, because earth is very rich in olivine, so we might be seeing these planets forming in a way that's very similar to Earth's past, if they form, when they form, once we find them.

Thomas Henning: Yeah, absolutely. I think as I said, the crystals tell us a lot about the thermal history of the systems, and one thing we also would like to find out is of course the ratio of carbon to oxygen, because from Earth we know that we have a very carbon poor planet. That sounds very strange, but it is the case compared to the carbon we could expect from the interstellar medium. We also have a very nitrogen poor planet. Again, something very surprising if you think about living systems, and we have to find out what the reason is what is carbon and nitrogen deficiency and one possibility is indeed that the carbon is somehow destroyed in these inner planet forming zones and in a number of objects we actually do not see a lot of carbon, but in the low mass stores, we do. So we have to study the diversity of planet forming regions and I think this diversity in composition may later be reflected in the diversity of compositions of exoplanets, which form in these environments.

Sarah Al-Ahmed: It was only recently I was speaking with one of the people on the team that detected phosphorus in the oceans of Enceladus and we got to a very deep conversation about the impacts that the distribution of carbon dioxide across a Solar System can have on what water is able to absorb and how it impacts these worlds. So understanding more of that carbon distribution could tell us a lot about those oceans if and when they form as well.

Thomas Henning: Absolutely, and I mean, we find it a lot of different molecules apart from water. We find CO, CO2, OH, HCN, disk around the low mass stars. We find C2H2 or benzenes, a large family of molecules and HCN is a particularly interesting molecule because it's a key molecule and origins of live field. It is often used as a molecule to produce amino acids, but also RNA precursors. HCN is really a molecule which is very close to my heart because of my interest in the origin's of life.

Sarah Al-Ahmed: This finding has some really interesting implications in the search for life because life as we know it requires water and the timeline for how these planets get water could change a lot. Can this result tell us anything about say the history of how water came to Earth?

Giulia Perotti: Yeah. Well, again, as I said, we are trying to understand what is the most dominant scenario for the origin of water in PDS 70 and being the star cooler and less massive than our sun, but still comparable it's really the best test bed that we have right now. What we also have to do is to combine the information that we obtained with JWST will also upcoming [inaudible] observations and in my opinion, and to be able to question further whether our oceans on Earth are mostly due to asteroid impacts or water coming from the inner disk. We also have to study, for example, the deuterium to hydrogen ratio. That would be an important piece in this puzzle to be able to answer. However, it's very difficult for PDS 70 or the star, which is so faint to be able to detect the deuterium and therefore estimate the deuterium to hydrogen ratio. But for other sources, for the stars that are brighter than PDS 70, that might be possible. So that would be a key question to answer in my opinion.

Sarah Al-Ahmed: I'm wondering, we can't actually do this, right? We can't take a planet and slice it in half and see what the entire planet is made of from the inside out. But if we did have a scenario where these planets formed with water with them in the disk, could that have any impacts on say the hydration of the minerals as you went into the planet? Would it have any impact that we could detect in its composition?

Giulia Perotti: We'll have to look at, for example, deuterium and to see if the isotopic anomalies that we detect on earth they resemble to the ones in the inner disk during the formation of terrestrial planets. It is challenging to do observationally speaking at the moment, but that would be a way to do it.

Thomas Henning: [inaudible] community is actively discussing what kind of meteorites or better asteroid material entered Earth early on. Was this more iron material or was it a material which is also carbon based and contain water. And at the moment I think there is no clear decision made, but if there was also a lot of water coming, then that would be a great connection to our own discovery. And I think you're completely right that the deuteration is a key element of the story, but also certainly the nitrogen isotopes. And the deuteration is important because our ocean water is actually not from this world. And what I mean with this is that it has a content of heavy water which can only be formed at very low temperatures. So we somehow have water which has a signature of low temperatures. And the question is, is this also true for the water in PDS 70 or for the water also just around young stars? And indeed in the NIRSpec wavelength range one could observe [inaudible] is a bit lucky and of course we hope to be lucky and have another nice discovery of deuterated water in the infrared. I think this will be very difficult for PDS 70, but we have a number of other targets which are very water rich and I guess should be possible.

Sarah Al-Ahmed: What other targets are upcoming in your studies on this?

Thomas Henning: I mean, one is for instance AA Tau, which is a very water rich source. We will get NIRSpec data, so in the infrared data, not only MIRI data, but the mid infrared and let's see if we find deuterated water in this system.

Sarah Al-Ahmed: That's an interesting point to make about the fact that the water on earth shows evidence that it formed somewhere else and migrated in. This could be a very complex situation where some of the water was already here when the planet formed and then on top of that, water from other places that formed in cooler environments then migrated in and created this interesting kind of cocktail of water from different locations.

Giulia Perotti: Some of the other targets that will be observed as part of the MINDS Survey are [inaudible] compared to PDS 70, which is faced on. And the fact of having this giant configuration means that with JWST we'd be able to probe the mid plains, really the region where planets are forming. And in the NIRSpec range we'll be able to study water, ice, so not only water vapor but also the composition of the dust grain. So that's also going to be a really important analysis, an important step of the program and general and answer question with the community, what is the abundance of water, ice in disks?

Sarah Al-Ahmed: That would be useful too because if it's [inaudible], it might be easier to detect the planets in that system instead of just seeing them directly as you did in this situation, but instead you could see them transit in front of their stars. Given the buzz around this, how do you think it might impact future research or funding priorities for JWST studies?

Thomas Henning: One thing we will certainly do is study the disk properties as a function of mass of central star. I mean most of the earth-like planets or rocky planets we find today are actually orbiting so-called M type stars. These are stars which are less massive than the sun and the disks around these stars are poorly investigated. And the reason is simply that our previous observatory like Spitzer, they were just not sensitive enough to do a good job. We only could investigate a few objects. So I think this is one thing we would like to do. The other thing we are already doing now is together with another colleague, the Solar System was probably formed in a cluster environment, but what I mean with this is that it wasn't formed alone, but there were a lot of stars around with a lot of UV light. And the question is, what is actually the composition of this in regions where we have such clustered star formation? Because all the nearby objects we observe are relatively isolated and we have observed such a disk and in this case we actually don't see a lot of difference. We see that the disk is much smaller than our disk, but [inaudible] disk composition seems to be similar. So I think to investigate these clusters will be another important goal.

Sarah Al-Ahmed: I'm really looking forward to it. I just cannot wait until we have so much information about these things that we're bored of studying exoplanetary systems and it just seems old hat. This kind of information, even just the plain detection of worlds when I was a child, was a thing that lit my imagination on fire to the point where point I dedicated my whole life to studying astronomy and astrophysics and planetary formation. These are the kinds of discoveries that inspire the future. So I'm really happy that you guys are dedicating so much time and thought to this.

Thomas Henning: I think we have a lot of fun.

Giulia Perotti: Yes, absolutely.

Thomas Henning: And JWST is a great machine. It is really working very, very well and so many people made it possible and I think we now have the [inaudible] and that's just wonderful.

Sarah Al-Ahmed: I'm really hoping that all of the studies that come out of JWST help us justify building more and more of these, maybe even a whole suite of them in different parts of the spectrum, just create a new system of great observatories based off of JWST, because this one telescope is completely changing so much of what we know about planetary formation and exoplanets in general, and we need more of this.

Thomas Henning: Yeah, I think the exoplanet community is also getting a lot of exciting results. And of course, it also paves the way for an observatory, which you may have in about 20 years from now, where we want to observe earth like planets directly and characterize the atmospheres, and at some point, we would like to look for evidence for live infrared spectroscopy or optical spectroscopy. So I think exciting times.

Sarah Al-Ahmed: Well, thank you both for joining me and for doing this amazing study, and I would love to hear more when you analyze more of these systems and might be able to make more comparisons between them, because this could really change the way we think about how water transports to these terrestrial worlds.

Thomas Henning: Thank you.

Giulia Perotti: Thank you very much, Sarah. It's been a great pleasure to be here on the Planetary Radio video.

Sarah Al-Ahmed: It's amazing how far the field of exoplanet studies has come. When I was born, we hadn't even discovered any planets outside of our Solar System yet. Just a few decades later, we've detected over 5,000 exoplanets and we can study the composition of proto-planetary disks hundreds of light years away. I can only imagine what discoveries lie ahead of us or what they might tell us about our place in space. There's a lot to look forward to. Now, let's check in with Bruce Betts, the chief scientist of The Planetary Society for what's up. Hey Bruce.

Bruce Betts: Hey Sarah.

Sarah Al-Ahmed: It's funny, earlier the show, I had an opportunity to talk to our latest intern from the Zed Factor Fellowship, Ariel, and I feel like her time with us completely disappeared. She came here in June and she's already done her whole time. How do things move so fast?

Bruce Betts: The relativistic time in our brains is something that I very much do not understand.

Sarah Al-Ahmed: But Ariel's new article was all about terminator zones and I realized we didn't actually get an opportunity to explain what Terminator zones are or what tidal locking is. As our chief scientist, would you mind explaining what title locking is and how that could make planets really weird for life?

Bruce Betts: Sure. Yes. So tidal locking is we have half the system tidally locked in our system with the moon always facing one side of it towards the Earth. It's basically when you get a large gravitational body and you get a small one hanging out near it, the small one gets grabbed by tides that it just wants to face one face always towards the face of the other face. I did not describe that very well, but bottom line is we can end up with a lot of tidal locking. Let's move on to the Pluto system, shall we? Because that's interesting, because Pluto and its large moon Charon or Karen are tidally locked in both respects so that Pluto always faces the same side to Charon as well as Charon always facing the same side to Pluto. And that's because they're somewhat comparable in size. Although Charon is smaller, it's a significant fraction. So over time, tides grab onto each other and because they're not perfect spheres but they have mass distributions, you can end up with this situation. Now, you go to a star system and if you put a planet close enough to a star, it will end up getting tidally locked. So it will always face one side of the star, which tends to make that side hot and crispy. As you get farther away from the parent star, you don't have enough tidal interaction to do tidal locking. So what Ariel's talking about is this recent research on M dwarf or red dwarf stars that are lower mass but still very massive and lower temperature. And so when you put a planet close enough to get tidally locked, you could conceivably come up with happy little temperatures except it gets tidally locked. So you end up crisping one side of the planet that's always facing the star and freezing the other side of the planet. But that's where we talk about the terminator. The terminator in planetary world is the line between day side and night side. It's between dark and light. Ooh, sounds kind of like something out of Star Wars. And so light side is getting fried and the dark side's getting frozen. And so people have now researched and she's talking about the fact that in between, you can, depending on the situation on the planet's surface, end up with a happy little temperature in between that might be stable. So you might have a strip following this terminator zone or you end up with the situation conducive to even having liquid water and therefore the potential for life. But it gets tricky, tricky, tricky. And she talks about the details, which I'll leave to the article. It's one of the first research papers focusing on this. So we'll see where the science evolves. But it's an interesting exercise to think that these planets that offhand you would say, "Oh, it's just bad for life, but maybe not if you have the right situation." How's that?

Sarah Al-Ahmed: It's good. I like that scientist is getting on this because I was introduced to this concept through sci-fi primarily, and I'm glad that you brought up Star Wars because when we posted this article in our member community, we actually had a member write in, it was Devon O'Rourke from Colorado who mentioned that the Twi'leks species in Star Wars was actually from a tidally lock planet and they only lived in the terminator zone. That's one example. I've read many books in sci-fi where they just live in this beautiful little twilight zone all the time, but woe one to you if you get too far away from that nice little temperature zone or you're either going to crisp or you're going to freeze.

Bruce Betts: Come with me if you want to be habitable.

Sarah Al-Ahmed: So funny you mentioned that because I was just watching Terminator two this last weekend. I think a bunch of people on staff ended up watching Terminator this weekend because of this article.

Bruce Betts: All right. Well, I'm sure this topic will recur and we'll be back.

Sarah Al-Ahmed: So what's our random space fact this week?

Bruce Betts: It seemed like a lot of facts, but let's go with the random space fact because that wasn't random and this is. We're talking dwarf planets and their friends, and so...

Sarah Al-Ahmed: You got to do your random space fact.

Bruce Betts: Oh my god, I'm so thrown off. Random space fact. So dwarf planets, we got Pluto, we got Eris, Haumea, Makemake and Ceres right now, but there are others that with more data, we'll probably end up being classified as dwarf planets. And in fact, interesting little point. This is really the kernel of the random space fact. There are four objects that in mass are more massive than Ceres or in diameter, I should say. And in mass are either more massive or very similar that are out there, which I'll have names that are either fun or very hard for me to pronounce. So we've got Gonggong, Quaoar-

Sarah Al-Ahmed: Quaoar.

Bruce Betts: I'm sorry. I believe the proper pronunciation is Quaoar-war-war-war-war-war-war-war. That's so not true. It's not true at all. I just enjoy saying that. It's kind of like when you talk about the ... cloud, I can't say it without doing that. So anyway, Gonggong, Quaoar, Sedna and then Charon itself is actually more massive considerably than Ceres and larger in diameter. And so there are other objects that are out there. Ceres being the smallest of the dwarf planets and the only asteroid in the gang. And even getting very, very close and this one's also can be fun, Orcus.

Sarah Al-Ahmed: Orcas,

Bruce Betts: Which has a moon. That's fun to say too. [inaudible] So anyway, as more data comes, look for more things to be classified as dwarf planets, there's more stuff. That's just what we found out past Neptune and the trans Neptunian objects. There's undoubtedly more good stuff out there. So whatever you call them, dwarf planets, planets, dwight, they're still quite intriguing, interesting and worlds that are big enough to be fascinating in and of themselves.

Sarah Al-Ahmed: I always try to mention that whenever people are sad that Pluto got reclassified. Pluto is one of the coolest dwarf planets. I'm not sad about it at all, especially knowing that it's tidally locked to Charon and Charon is tidally locked to it. They're doing this beautiful kind of almost romantic dance in space together.

Bruce Betts: Yeah, no, there's all sorts of good interesting stuff going out there. Too bad it's so hard to observe, but we're getting better.

Sarah Al-Ahmed: I also wanted to share with you, Bruce, and with everyone else, that this is the first week that we did our space trivia contest in our member community. And I've been really grateful for people's feedback on it because it's been a lot of fun. And this week we actually got to do a multiple choice question, so I'm really looking forward to doing more of this in the future. We had some people write in and say that this was just one more reason why they feel like The Planetary Society community is one of the best places that they've been. Between that and our book club, I feel like it's a really good time. So if anybody wants to join us in the community, just need to be a Planetary Society member and you can check it out at or download our app. We have an app now.

Bruce Betts: We have an app?

Sarah Al-Ahmed: We have an app for that.

Bruce Betts: All right. That's cool. All right, everybody, go out there. Look up the night sky, think about dolphins going along just past the surf line, chilling hard, flipping around, and being dolphins. Thank you and goodnight.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week to discuss the slow evolution of Jupiter's Moon Europa. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our curious members. You can join us as we puzzle over the formation and beauty of the worlds around us at Mark Hilverda and Ray Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. And until next week, ad astra.